1. Field of the Invention
The present invention relates to a capacitor for incorporation in a wiring board and a wiring board having the same. Furthermore, the present invention concerns a wiring board having a structure in which a ceramic chip for embedment is embedded in an accommodating hole portion of a board core, and a buildup layer is formed by being laminated on its surface, as well as a method of manufacturing the same, and a ceramic chip for embedment.
2. Description of the Related Art
In recent years, the speed of the operation of semiconductor chips is becoming increasingly higher due to advancement in the integrated circuit technology. In conjunction with this trend, there are cases where noise is superimposed on the power source wiring and the like, possibly resulting in erroneous operation. Accordingly, a capacitor is mounted on an upper surface or a lower surface of a wiring board on which the semiconductor chip is mounted, so as to eliminate the noise.
With the above-described technique, however, since it is necessary to mount the capacitor separately after the completion of the wiring board, the number of processes disadvantageously increases. In addition, there is a need to secure in advance a region where the capacitor is mounted on the wiring board, so that the freedom of the layout of other electronic components declines. Furthermore, because the region where the capacitor is mounted on the wiring board is restricted by other wiring and the like, the wiring distance between the capacitor and the semiconductor chip becomes long, so that the wiring resistance and inductance become disadvantageously large.
For these reasons, a technique for incorporating the capacitor in the wiring board has been proposed. Here, the interior of an insulating layer formed on a core board is considered as one possible place where the capacitor is disposed in this technique, since the wiring resistance and inductance can be reduced further if the capacitor is brought close to the semiconductor chip.
In this case, however, it becomes important to ensure adhesion between the capacitor and the insulating layer, but since a ceramic is exposed in large portions of the obverse surface and the reverse surface of a conventional capacitor, the adhesion between the capacitor and the insulating layer is insufficient. As a result, a gap is created between the capacitor and the insulating layer due to delamination and the like, possibly causing faulty conduction.
It should be noted a technique has been disclosed in which a capacitor is incorporated in the insulating layer formed on a substrate, but there has been no disclosure as to the adhesion between the capacitor and the insulating layer and means for improving the adhesion (e.g., refer to JP-A-2004-228190).
Semiconductor integrated circuit devices (IC chips) used in CPUs of computers in recent years tend to be characterized by increasingly higher speed and higher functions, and the number of terminals tends to increase and the pitch between the terminals tends to become narrower correspondingly. Generally, a multiplicity of terminals are densely arranged in array form on the bottom surface of the IC chip, and such terminal groups are connected to terminal groups on the motherboard side in flip chip form. However, since there is a large difference in the terminal pitch between the terminal groups on the IC chip side and the terminal groups on the motherboard side, it is difficult to directly connect the IC chip onto the motherboard. For this reason, a technique is generally adopted in which the IC chip is mounted on a wiring board for IC chip mounting, and the wiring board for IC chip mounting is mounted on the motherboard. As the wiring board for IC chip mounting of this type, those have hitherto been proposed in which a ceramic chip is embedded in a core board formed of a polymeric material to form a core portion, and buildup layers are respectively formed on the obverse surface and the reverse surface of the core portion (e.g., refer to JP-A-2005-39217 and JP-A-2005-39243).
The above-described conventional wiring board for IC chip mounting is manufactured, for instance, in the following procedure. First, a board core is prepared which is formed of a polymeric material and has accommodating hole portions which are respectively open in both the obverse surface and the reverse surface of the core. Also, a ceramic chip for embedment is prepared in which a plurality of terminal electrodes are projectingly provided on the obverse surface and the reverse surface, respectively, of the chip. Next, a taping step is carried out in which an adhesive tape is attached to the reverse surface side of the core, and the opening on the core reverse surface side of the accommodating hole portion is sealed in advance. Then, an accommodation step for accommodating the ceramic chip for embedment in the accommodating hole portion is carried out, and the reverse surface of the chip is attached to the adhesive surface of the adhesive tape to temporarily fix it. Then, a fixing step is carried out in which a filler is filled in the gaps between inner surfaces of the accommodating hole portion and side surfaces of the ceramic chip for embedment, and is subsequently cured, thereby fixing the ceramic chip for embedment in the board core. Subsequently, the formation of an interlayer insulating layer having a polymeric material as a principal constituent and the formation of a conductor layer are alternately performed on each of the obverse surface and the reverse surface of the core portion which is constituted by the board core and the ceramic chip for embedment, thereby forming the buildup layers. As a result, a desired wiring board for IC chip mounting can be obtained.
3. Problems to be Solved by the Invention
The present invention has been devised to overcome the above-described problems, and an object of the invention is to provide a capacitor for incorporation in a wiring board which makes it possible to reduce faulty conduction in the case where the capacitor is incorporated in the wiring board, as well as a wiring board incorporating this capacitor for incorporation in a wiring board.
In the case of the above-cited JP-A-2005-39217 and JP-A-2005-39243, the obverse surface of the ceramic chip is exposed on the obverse surface of the core portion, while the reverse surface of the ceramic chip is exposed on the reverse surface of the core portion. For this reason, a portion of the interlayer insulating layer constituting the buildup layer is formed on not only the board core but also the ceramic chip. However, in the case of the above-described conventional wiring board for IC chip mounting, it is difficult to ensure high adhesive strength between the interlayer insulating layer and the ceramic chip which constitute the buildup layer. Accordingly, there is a possibility of the occurrence of the lifting up or delamination of the buildup layer, so that there has been a problem in that high reliability cannot be imparted. Particularly in recent years, the amount of heat generated tends to increase in conjunction with trends toward high-speed and high-function IC chips, and therefore the effect of thermal stress imparted to the buildup layer also tends to increase. Hence, the circumstances are such that the lifting up or delamination of the buildup layer is more likely to occur.
In addition, in the case of the above-described conventional technique, since a plurality of terminal electrodes are projectingly provided, irregularities are produced on the obverse surface and the reverse surface of the ceramic chip. However, there has been a problem in that if such irregularities are present, the effect of these irregularities affects the obverse surface of the buildup layer, and the flatness declines, thereby making it difficult to mount the IC chip.
The present invention has also been devised in view of the above-described problem, and another object of the invention is to provide a wiring board excelling in the adhesive strength between the interlayer insulating layer and the ceramic chip for embedment which constitute the buildup layer, as well as a method of manufacturing the same. A still another object of the invention is to provide a ceramic chip for embedment suitable for use in a wiring board.